The layered silicates to which the invention is applicable are of the type which can be represented by the general formula E.sub.i M.sub.x Si.sub.y O.sub.n (OH).sub.m where M is Al, Mg, or Fe, x =2 to 6; y =2 to 8, n =2 to 20, m =0 to 8, and E.sub.i is one or more exchangeable ions (K, Na, Mg, Ca, Ba, Fe, Li, etc.). These layered silicates will hereinafter in this specification be referred to as "layered lattice silicates".
In the instance of layered lattice silicates such as kaolin clays, it has long been recognized that products having new properties and uses could be formulated by combining these aluminosilicates with organic materials. However, useful progress in this direction has tended to be limited by the lack of available covalent bonding at the mineral/organic interface. In the past this difficulty has been partially overcome by surface modification of the kaolinite through coupling with organosilane compounds, and subsequent reaction between dependent silanes and organics.
Thus, in Papalos, U.S. Pat. No. 3,227,675, for example, kaolin clays are described, the surfaces of which are modified with organofunctional silanes. A typical such agent, e.g., is a methacryloxypropyltrimethoxy silane. The kaolin clays so modified are advantageously used as fillers for natural and synthetic rubbers and the like. It is also pointed out in this patent that such modified products can serve as intermediates for synthesis of new pigments, which are useful as fillers for polymers, elastomers and resins. This result obtains because the silanes used to modify the kaolin clays are di- or polyfunctional, and only one functional group, the silane, is attached to the clay, leaving the remaining reactive groups to react further.
Additional references of this type include Iannicelli U.S. Pat. No. 3,290,165, and Iannicelli, U.S. Pat. No. 3,567,680.
However, the modification of aluminosilicates such as kaolin clays by the use of organosilanes, is a complicated and expensive process. Among other things, the cost of the organosilane itself is very high. Furthermore, the resulting products have only limited capability for further reaction, regardless of the particular organosilanes utilized. Also, when used in perhaps the most common application, i.e. as fillers in polymer systems, the limited number of available structures tends to impose limitations on the compatibility of such organosilanemodified pigments with various polymer matrices.
U.S. Pat. No. 3,397,171 describes a process for the production of polyamide textile fibers in which a small percentage of a kaolinite is added to polycarbonamide-forming reagents plus a deflocculant and the mixture is then polymerized. It is mentioned, however, that microscopic inspection reveals that each kaolinite platelet is surrounded by an elongated void where the polymer has separated from the particle, so that evidently no bonding has occurred by use of this process.
In U.S. Pat. No. 3,912,532 particles of a clay such as kaolin are coated with a urea-formaldehyde resin by dispersing the clay particles in an aqueous solution of a prepolymer of urea-formaldehyde and then polymerizing the latter. The products are used as opacifying agents for paper.
U.S. Pat. No. 4,230,501 describes compositions of pigments such as carbon black mixed with a combination of waxy materials and wax-like materials. The products are said to be dispersible in plastics.
According to U.S. Pat. No. 4,091,164, normally hydrophilic inorganic fillers such as kaolin clays are modified to enhance their dispersibility in polymeric resins by admixing filler particles with a block copolymer of ethylene oxide and propylene oxide under shear and at elevated temperature to coat the filler particles with the block copolymer.
In U.S. Pat. No. 4,349,389 an inorganic pigment such as titanium dioxide, suitably as an aqueous slurry, is coated with a substance which renders the surface hydrophobic, such as dispersing agents of the type of alkylbenzene sulfonic acids, and then with a thermoplastic polymer which may be used as a mixture with an emulsifying agent. The products are said to be dispersible in thermoplastics and paints.
U.S. Pat. No. 3,573,944 describes a process of forming organophilic particles from a clay such as kaolin, by heating to drive off bound water, cooling, adding a solution in a petroleum ether solvent of an alkylene divinyl ether and polymerizing said ether while refluxing the solvent.
U.S. Pat. No. 3,901,845 describes filled and reinforced polyamide (e.g. nylon 6 or nylon 6,6) compositions in which a mineral filler such as silica is chemically coupled to the polymer matrix by an aromatic compound having a carboxyl group and a hydroxyl or amine group.
In accordance with the foregoing, it may be regarded as an object of the present invention, to provide new types of surface modified layered lattice silicate pigments, which are totally and directly compatible with the polymer systems to which they may be added as fillers, and which when so used provide outstanding improvements in the mechanical and other useful properties of the filled system.
It is also an object of the invention to provide a method of surface modification of layered lattice silicates in which improved bonding of modifier to the silicate surface is achieved.
It is a further object of the invention to provide a relatively simple, and effective process, for preparing the aforementioned surface modified pigments from layered lattice silicates, such as aluminosilicates, and which enables preparation of such products with a wide variety of compatibility characteristics for use in desired polymer matrices.